Page 29 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Exposure to Computer Disciplines

Notes channels to access secondary storage and transfers the desired data using intermediate area
in primary storage. Secondary storage does not lose the data when the device is powered
down-it is non-volatile. Per unit, it is typically also two orders of magnitude less expensive
than primary storage. Consequently, modern computer systems typically have two orders
of magnitude more secondary storage than primary storage and data is kept for a longer
time there.

In modern computers, hard disk drive are usually used as secondary storage. The time taken
to access a given byte of information stored on a hard disk is typically a few thousandths of a
second, or milliseconds.
2.3.2.1 Magnetic Tape

Magnetic tapes are used for large computers like mainframe computers where large volume
of data is stored for a longer time. In PC also you can use tapes in the form of cassettes.
The storage of data in tapes is inexpensive. Tapes consist of magnetic materials that store
data permanently. It can be 12.5 mm to 25 mm wide plastic film-type and 500 meter to
1200 meter long, which is coated with magnetic material. The tape unit is connected to the
central processor and information is fed into or read from the tape through the processor.
It is similar to a cassette tape recorder.

Figure 2.6: Magnetic Tapes

Advantages of Magnetic Tape
Compact: A 10-inch diameter reel of tape is 2400 feet long and is able to hold 800, 1600 or 6250
characters in each inch of its length. The maximum capacity of such tape is 180 million characters.
Thus data are stored much more compactly on tape.

Economical: The cost of storing data is very less as compared to other storage devices.
Fast: Copying of data is easier and fast.
Long term Storage and Re-usability: Magnetic tapes can be used for long term storage and a
tape can be used repeatedly with out loss of data.
2.3.2.2 Magnetic Disk

You might have seen the gramophone record, which is like a circular disk and coated with magnetic
material. Magnetic disks used in computer are made on the same principle.

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